From: "BertramScharpf (Bertram Scharpf)" <software@...>
Date: 2013-11-14T21:48:22+09:00
Subject: [ruby-core:58336] [ruby-trunk - Feature #9108] Hash sub-selections


Issue #9108 has been updated by BertramScharpf (Bertram Scharpf).


=begin
(({
[:dog, :cat].map { |k| sounds[ k] }
#=> ["woof", "meow"]
}))

(({
[:dog, :cat].inject Hash.new do |r,k| r[ k] = sounds[ k] ; r end
#=> {:dog=>"woof", :cat=>"meow"}
}))

If you look at it this way, one should rather define an Array method than
a Hash method.

=end

----------------------------------------
Feature #9108: Hash sub-selections
https://bugs.ruby-lang.org/issues/9108#change-42933

Author: wardrop (Tom Wardrop)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
Hi,

I seem to regularly have the requirement to work on a sub-set of key/value pairs within a hash. Ruby doesn't seem to provide a concise means of selecting a sub-set of keys from a hash. To give an example of what I mean, including how I currently achieve this:

    sounds = {dog: 'woof', cat: 'meow', mouse: 'squeak', horse: 'nay', cow: 'moo'}
    domestic_sounds = sounds.select { |k,v| [:dog, :cat].include? k } #=> {dog: 'woof', cat: 'meow'}

I think a more concise and graceful solution to this would be to allow the Hash#[] method to take multiple arguments, returning a sub-hash, e.g.

    domestic_sounds = sounds[:dog, :cat] #=> {dog: 'woof', cat: 'meow'}

I had a requirement in the current project I'm working on to concatenate two values in a hash. If this proposed feature existed, I could of just done this...

    sounds[:dog, :cat].values.join #=> 'woofmeow'

You could do something similar for the setter also...

    sounds[:monkey, :bat] = 'screech'
    sounds #=> {dog: 'woof', cat: 'meow', mouse: 'squeak', horse: 'nay', cow: 'moo', monkey: 'screech', bat: 'screech'}

Concise, convenient and readable. Thoughts?

=end


-- 
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